<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .a {
      color: red;
    }
    .b {
      color: green;
    }
  </style>
</head>
<body>

<p class="b a">this is a p</p>
</body>
</html>